JPH06237425A - Method and circuit for detecting audio signal - Google Patents

Abstract

PURPOSE:To obtain the method and circuit for detecting an audio signal which prevents effect of noise without provision of a mute circuit and incurs no cost- increase. CONSTITUTION:When an AM audio signal is outputted, a microcomputer 12 allows an FM detection circuit 10 to detect an FM intermediate frequency signal (FM SIF) while it is tuned to an AM intermediate frequency signal (AM SIF). Thus, even when an output of the FM detection circuit 10 is fed to an audio switch 8, no crosstalk is caused to the AM audio signal. Thus, the effect of noise is prevented without provision of a mute circuit having been required for a conventional circuit and the cost is not increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio signal detection method and circuit suitable for use in, for example, a multi-standard system television for receiving European television broadcasting.

[0002]

2. Description of the Related Art In a multi-standard system television for receiving a European television broadcast, an audio signal amplitude-modulated according to a receiving channel (hereinafter referred to as an AM audio signal) or a frequency-modulated audio signal. (Hereinafter, a broadcast wave audio signal is referred to as an FM audio signal)
An AM detector and an FM detector are provided to demodulate either of the above. Then, in a reception mode (SYSTEM L) for AM detection of an audio intermediate frequency signal, AM audio reception is performed by an AM detector, while a reception mode (SYSTEM B / G, I,
In D / K), FM sound is received by the FM detector.

FIG. 3 is a block diagram showing the structure of an audio signal detection circuit in such a multi-standard system television. In this figure, 6 is a filter, which is a filter for extracting and outputting only the AM intermediate frequency signal supplied from a tuner unit (not shown).
An AM detection circuit 7 detects the output signal of the filter 6 and outputs an AM audio signal. Reference numeral 8 is an audio switch. The audio switch 8 switches between an AM audio signal supplied to one input end and an FM audio signal supplied to the other input end in accordance with a switch signal supplied from the outside to a subsequent stage. Output.

A bandpass filter 9 outputs a predetermined band component of the FM intermediate frequency signal to the next stage. An FM detection circuit 10 detects the output signal of the bandpass filter 9 and outputs an FM audio signal. In addition, the FM detection circuit 10 receives a reception mode (SYSTEM B / SYSTEM) corresponding to a mode instruction signal supplied from the microcomputer 12.
G), the detection operation is performed in the reception mode (SYSTEM I) and the reception mode (SYSTEM D / K). 11 is
This is a mute circuit that mutes the noise output from the FM detection circuit 10 in the reception mode SYSTEM L. The mute circuit 11 is provided with an FM detection circuit 10 when a mute instruction signal is supplied from the microcomputer 12.
Is configured to mute the noise output by. A microcomputer 12 controls the entire multi-standard system television, and generates the above-mentioned switch signal, mode instruction signal and mute instruction signal in accordance with the reception mode.

In such a configuration, when receiving AM audio, the microcomputer 12 supplies a switch signal for selecting the AM audio signal to the audio switch 8 and a mute instruction signal for muting the FM audio signal. It is supplied to the mute circuit 11. As a result, the mute circuit 11 mutes the FM audio signal,
Since the audio switch 8 outputs the AM audio signal to the next stage, AM audio is received. On the other hand, when receiving FM audio, the F
A switch signal for selecting the M audio signal is supplied, and a mode instruction signal for specifying the reception mode is supplied to the FM detection circuit 10. As a result, the FM audio signal detected in the predetermined reception mode is output to the next stage via the audio switch 8.

[0006]

By the way, in the above-described conventional audio signal detection circuit, when the AM audio reception operation is performed without the mute circuit 11 being muted, the output of the FM detection circuit 10 is superimposed on the AM audio signal, It becomes a noise source.
Further, if the separation characteristic of the audio switch 8 that performs the signal switching operation under the control of the microcomputer 12 is poor, the output of the FM detection circuit 10 cross-talks with the AM audio signal, which also causes noise. . Therefore, in the conventional audio signal detection circuit, the mute circuit 11 is an indispensable constituent element in order to prevent the influence of such noise. If the mute circuit 11 is not provided, the audio switch 8 having good separation characteristics is required.

However, when the mute circuit 11 is provided in the audio signal detection circuit, a peripheral circuit for turning the mute circuit 11 on and off in accordance with the mute instruction signal is required, which causes an increase in cost. is there. On the other hand, when omitting the mute circuit 11,
Audio switch 8 with excellent separation characteristics
Is required, and in this case as well, it has been a factor that invites an increase in cost. Therefore, the present invention has been made in view of the above-mentioned circumstances, and provides an audio signal detection method and circuit that can prevent the influence of noise without providing a mute circuit and that does not invite an increase in cost. Has an aim.

[0008]

In order to achieve the above object, according to the invention as set forth in claim 1, an A voice signal is generated by detecting the amplitude-modulated first intermediate frequency signal.
The M detection process, the FM detection process of detecting the frequency-modulated second intermediate frequency signal to generate the FM sound signal, and the AM sound signal or the FM sound signal of the FM sound signal according to the switching signal supplied from the outside. And a switching control process for selecting and outputting either one of them.
When selecting and outputting the M audio signal, it is characterized in that the FM detection process is synchronized with the first intermediate frequency signal to perform a detection operation.

According to a second aspect of the present invention, an AM detection means for detecting the amplitude-modulated first intermediate frequency signal to generate an AM audio signal, and a frequency-modulated second intermediate frequency signal. The FM detection means for detecting a signal to generate an FM audio signal, and the above A according to a switching signal supplied from the outside.
A switching control means for selecting and outputting either the M audio signal or the FM audio signal is provided, and the switching control means, when outputting the AM audio signal, the FM audio signal.
The detection means is tuned to the first intermediate frequency signal to perform a detection operation.

[0010]

In the present invention, when an AM audio signal is output,
The switching control means tunes the FM detection means to the first intermediate frequency signal for detection operation. This prevents the FM detection output from cross-talking to the AM audio signal.
Therefore, even if the mute circuit is not provided, the influence of noise can be prevented, and the cost does not increase.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of a television of a multi-standard system using an audio signal detection circuit according to the present invention. In this figure,
Reference numeral 1 denotes a high frequency signal received via an antenna ANT, which is a video intermediate frequency signal or an AM audio intermediate frequency signal (AM S
It is a tuner for converting to (IF) and outputting. Reference numeral 2 is a video intermediate frequency amplifier circuit (VIF), which outputs the video intermediate frequency signal supplied from the tuner 1 as a video signal to the next stage, and the QPT output of this VIF as an FM audio intermediate frequency signal (FM SIF). Occur.

Reference numeral 3 is a Y / C separation circuit, and 4 is an audio signal detection circuit (SIF). The audio signal detection circuit 4 AM-detects the AM audio intermediate frequency signal (AM SIF) or the FM audio intermediate frequency signal (FM SIF) according to the operation mode to AM audio signal or FM-detects the FM audio signal.
Generates an audio signal. Reference numeral 5 denotes an amplifier, which amplifies the AM audio signal or the FM audio signal and supplies it to the speaker SP.

Next, FIG. 2 is a block diagram showing the configuration of the above-mentioned audio signal detection circuit (SIF) 4. In this figure, parts common to the parts shown in FIG. 3 are assigned the same reference numerals and explanations thereof are omitted. The configuration shown in FIG. 2 is different from the conventional example shown in FIG. 3 in that the mute circuit 11 is omitted and the influence of noise during AM voice reception is prevented by the operation of the microcomputer 12. . In the following, this audio signal detection circuit (S
The detection operation of the IF) 4 will be described.

Operation for Receiving FM Audio Signal In this case, the above-mentioned FM detection circuit 10 is instructed to the microcomputer 12 by any one of the reception modes (SYSTEM B / G, SYSTEM I, SYSTEM).
EM D / K) performs detection operation. Further, the audio switch 8 operates so as to select the output of the circuit 10 according to an instruction from the microcomputer 12. As a result, the audio signal detection circuit (SIF) 4 is connected to the Q of VIF2.
FM SIF supplied as PT output is FM detected,
The FM audio signal thus obtained is output to the next stage via the audio switch 8.

Operation when AM voice signal is received Next, a reception mode (SYSTE) for receiving an AM voice signal
In ML), the AM audio intermediate frequency signal (AM SIF) output from the tuner 1 is filtered, detected by the AM detection circuit 7, and supplied to the audio switch 8 as an AM audio signal.

At this time, the audio signal detection circuit (SIF) 4 outputs a 6.5 MHz AM as the QPT output of VIF2.
The audio intermediate frequency signal and the video signal are supplied to the FM detection circuit 10 via the bandpass filter 9. Then, the AM audio intermediate frequency signal and the video signal are F
The M detection causes noise, which causes crosstalk with the AM audio signal in the audio switch 8.

Therefore, in order to remove such interference, the microcomputer 12 instructs the FM detection circuit 10 to
A mode instruction signal is supplied so that the detection operation is performed in the reception mode (SYSTEM D / K). As a result, the circuit 10
Is set to an operation mode in which an FM signal of 6.5 MHz is detected. Therefore, the FM detection circuit 10 is 6.5M.
Since the AM signal / video signal of Hz and the FM signal of 6.5 MHz are detected, the detection output is lost. That is, F
That is, the output of the M detection circuit 10 does not become a noise source, and there is no need to mute.

As described above, according to the above-mentioned embodiment, A
When the M intermediate frequency signal is detected to generate the AM audio signal, the FM intermediate frequency signal is tuned to the AM intermediate frequency signal to be detected and the FM detection is performed. Therefore, the FM detection output crosses the AM audio signal. No more talking. Therefore, even if the mute circuit is not provided, the influence of noise can be prevented, and the cost does not increase. It should be noted that such a receiving operation can be handled only by changing the control program of the microcomputer 12.

[0019]

As described above, according to the present invention,
When the AM voice signal is received, the switching control means performs the detection operation by synchronizing the FM detection means with the first intermediate frequency signal, so that the FM detection output does not cross-talk with the AM voice signal. As a result, the influence of noise can be prevented without providing a mute circuit. Moreover, such a thing does not invite cost increase.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment according to the present invention.

FIG. 2 is a sound signal detection circuit (SIF) in the same embodiment.
3 is a block diagram showing the configuration of FIG.

FIG. 3 is a diagram for explaining a conventional example.

[Explanation of symbols]

 6 ... Filter (AM detection means) 7 ... AM detection circuit (AM detection means) 8 ... Audio switch (switch control means) 9 ... Band pass filter (FM detection means) 10 ... FM detection circuit (FM detection means) 12 ... Micro Computer (switch control means)

Claims (4)

[Claims] 1. An AM detection process for detecting an amplitude-modulated first intermediate frequency signal to generate an AM audio signal and an AM detection process for detecting a frequency-modulated second intermediate frequency signal to generate an FM audio signal. An FM detection process and a switching control process for selecting and outputting either the AM audio signal or the FM audio signal according to a switching signal supplied from the outside, and the switching control process includes the AM controlling process. A method for detecting a voice signal, characterized in that, when a voice signal is selected and output, the FM detection process is tuned to the first intermediate frequency signal to perform a detection operation. 2. An AM detection means for detecting an amplitude-modulated first intermediate frequency signal to generate an AM audio signal, and an AM detection means for detecting a frequency-modulated second intermediate frequency signal to generate an FM audio signal. An FM detection means and a switching control means for selecting and outputting either the AM audio signal or the FM audio signal according to a switching signal supplied from the outside are provided, and the switching control means includes the AM audio signal. An audio signal detection circuit characterized in that, when a signal is output, the FM detection means is tuned to the first intermediate frequency signal to perform a detection operation. 3. A multi-standard type television for detecting an amplitude-modulated first intermediate frequency signal and a frequency-modulated second intermediate frequency signal to generate an AM audio signal or an FM audio signal, respectively. 3. The audio signal detection circuit according to claim 2, wherein when the AM audio signal is generated, the FM detection means is tuned to the first intermediate frequency signal to perform an FM detection operation. 4. A television for detecting an amplitude-modulated first intermediate frequency signal to generate an AM audio signal and detecting a frequency-modulated second intermediate frequency signal to generate an FM audio signal. It is provided in the intermediate frequency block and
3. The audio signal detection circuit according to claim 2, wherein when outputting the M audio signal, the FM detection means is tuned to the first intermediate frequency signal to perform an FM detection operation.